[sensors](Linux) Fix tsan data race in sensor reader

device/generic_sensor/platform_sensor_reader_linux.h

Index: device/generic_sensor/platform_sensor_reader_linux.h
diff --git a/device/generic_sensor/platform_sensor_reader_linux.h b/device/generic_sensor/platform_sensor_reader_linux.h
index 755ad2671af5f80937cd470d8f3ac8851d64f733..b2a224461c044ed599f647545813df0496173924 100644
--- a/device/generic_sensor/platform_sensor_reader_linux.h
+++ b/device/generic_sensor/platform_sensor_reader_linux.h
@@ -19,29 +19,33 @@ class PlatformSensorConfiguration;
 struct SensorInfoLinux;
 
 // A generic reader class that can be implemented with two different strategies:
-// polling and on trigger.
+// polling and on trigger. All methods except SetPlatformSensorLinux
+// are not safe and must be called on the same thread which this reader belongs
+// to.
 class SensorReader {
  public:
   // Creates a new instance of SensorReader. At the moment, only polling
   // reader is supported.
   static std::unique_ptr<SensorReader> Create(
       const SensorInfoLinux* sensor_device,
-      PlatformSensorLinux* sensor,
-      scoped_refptr<base::SingleThreadTaskRunner> polling_thread_task_runner);
+      scoped_refptr<base::SingleThreadTaskRunner> task_runner);
 
   virtual ~SensorReader();
 
   // Starts fetching data based on strategy this reader has chosen.
   // Only polling strategy is supported at the moment. Thread safe.
-  virtual bool StartFetchingData(
+  virtual void StartFetchingData(
       const PlatformSensorConfiguration& configuration) = 0;
 
   // Stops fetching data. Thread safe.
   virtual void StopFetchingData() = 0;
 
+  // Sets sensor that this reader reports to. Must be called only once.
+  // Thread safe.

[gab, 2016/12/14 14:52:21]

From the implementation this isn't "thread-safe", it's only fine as-is because
it's called before the SensorReader is active.

i.e. you want something like:

// // Sets sensor that this reader reports to. Must be called after the
SensorReader is constructed, before tasks are posted to it from another
sequence.

+  void SetPlatformSensorLinux(PlatformSensorLinux* sensor);
+
  protected:
-  SensorReader(PlatformSensorLinux* sensor,
-               scoped_refptr<base::SingleThreadTaskRunner> polling_task_runner);
+  SensorReader(scoped_refptr<base::SingleThreadTaskRunner> task_runner);
 
   // Notifies |sensor_| about an error.
   void NotifyReadError();